A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.
Screening apparatus of the type with which the invention is concerned is generally used for screening, grading, or separating materials such as mining ores and comprises an array of screen panels which are removably fixed to a frame to provide a continuous screen deck. The material to be screened is fed onto the deck at one end and the apparatus is vibrated so that the material moves over and through its screening surface.
One form of screen panel includes a steel frame moulded within a resilient plastic material, such as polyurethane. See for an example of such a screen panel, Australian Patent No. 577767 (66006/86). The plastic moulding forms the major part of the panel and it is in the plastic moulding that the openings for screening are provided. The steel frame provides rigidity to the screen panel.
Other forms of screen panels include an assembly which comprises a hard plastic frame and a separate rubber or polyurethane screen surface that is releasably attached to the frame. In this arrangement, the plastic frame can be attached to the subframe of a vibratory screening machine first and the rubber or polyurethane screen surface can then be attached to the plastic frame. Alternatively, the polyurethane screen surface can be attached to the plastic frame first and the assembly can then be attached to the subframe of the vibratory machine. The advantage of a panel assembly of this kind is that the assembly is generally more flexible and is generally less expensive than the encapsulated steel frame version discussed above, because the screen surface can be replaced without necessarily also replacing the frame. The assembly also provides flexibility in the combination of frame and screen surface, given that various different grades of screen surfaces, ie harder or softer, or with larger or smaller screening apertures, can be attached to the one form of frame. These forms of assembly can include a polyurethane or rubber coated steel or plastic frame in which the screen surface is formed by the polyurethane or rubber coating.
In the panel assembly described above, care must be taken in the design of the frame and screen surface, in particular in relation to the connection between them, given that in use, with the panel assembly applied to the deck of vibratory machinery, the panel assembly will be subject to significant vibration and the screen surface can disconnect or release from the frame if the connection between them is not sufficiently secure.
In all forms of screening apparatus, the material being screened (ores for example) causes the screen panels to wear over time, due to the abrasiveness of the ores or materials typically being screened, and thus the screen panels require periodic replacement. Replacement causes downtime of the vibratory machinery and loss of output of the mine. Accordingly, the ease and speed of replacement of the worn parts (either just the screen surface, or the screen surface and the frame to which the screen surface is attached) is of significant importance to the mine operator. It follows therefore that screen panels should be relatively easy to fit to and remove from the subframe of a vibratory machine.
As indicated above, in some installations, the operators of the vibratory machinery will remove only the screen surface of the panel assembly when sufficient wear of the screen surface has taken place, rather than removing both the frame and the screen surface for replacement. Thus, the panel assembly is configured so that removal of the screen surface only, rather than removal of the screen surface and the frame, is possible. This reduces the cost for the mine operator because the frame is not replaced, but the saving is only useful if a new screen surface can be fitted to the existing frame that remains connected to the vibratory machinery quickly and easily, so that time lost in downtime of the vibratory machinery is not more than would have been experienced with replacement of the complete panel assembly (comprising the screen surface and the frame).
Systems have been developed in the past for fixing screen panels to the subframe of a vibratory machine, whereby individual panels can be removed and replaced when worn. In applicant's Australian Patent No. 2012201297, a system has been developed in which panels can be fixed to vibratory machinery along a pair of opposite edges. The arrangement disclosed allows for a small amount of adjustment movement of the panels as they are applied to a deck to ensure close fitting and alignment between adjacent panels. In the arrangement of Patent No. 2012201297, the panels are securely fixed to the subframe of the vibratory machine by engagement along a major portion of the opposite sides of the respective panels with elongate fixing members that connect to the subframe itself. The extent of engagement between the panels and the elongate fixing members provides for very secure connection between the panels and the subframe.
The present invention has been developed with the above form of screening apparatus of applicant's Patent No. 2012201297 in mind, although it should be appreciated that the invention could have wider use with other forms of screening apparatus and screen panels.